1. Field of the Invention
This invention relates to balloons and to balloon catheters which are useful in medical dilatation procedures and is more particularly concerned with the development of a collapsible dilatation balloon that can withstand significant inflation pressures and upon deflation avoids the problem of "winging", that is the development of flat, lateral portions projecting laterally outward beyond the rest of the catheter.
2. Description of the Prior Art
Balloon catheters are finding increasing use in medical procedures such as percutaneous transluminal angioplasty, percutaneous transluminal nephrostomy, ureteral dilatation, biliary duct dilatation, percutaneous transluminal renal angioplasty, and the like. Balloons for use in these procedures have been prepared from a variety of polymeric materials which are blood and tissue compatible. Among those materials that have been employed include materials such as poly(vinylchloride), polyethylene and the like, homopolymers or copolymers of olefins, polyethylene/vinyl acetate copolymers, polyethylene terepthalate and polyurethanes.
Catheter balloons must be quite strong to withstand significant inflation pressures. Accordingly, they sometimes tend to be somewhat stiff, since their wall thickness must be sufficient to provide the necessary strength. Thus, when deflated, such catheter balloons can flatten in a phenomenon known as "winging", in which the flat, lateral portions of the deflated balloon project laterally outward beyond the rest of the catheter. This is deemed to be undesirable by many practitioners because of a concern that the flat wings may damage, e.g. an artery wall, as the deflated balloon is removed from the arterial system. Also, such flat wings can interfere with the manipulation of the catheter and its easy advancement through the arterial system.
A recent attempt to solve the problem of winging has been reported in U.S. Pat. No. 4,941,811, which describes a balloon catheter wherein the balloon defines transition zones at the respective ends which are of a rounded fluted shape. The flutes, typically from three to eight, are described as generally longitudinally directed at an angle to the balloon axis, and typically extending at a mutually perpendicular radial angle to the axis, the lateral angle being generally from 0 to about 45 degrees, preferably about 10 to 30 degrees. The radial angle in the as-molded balloon is described as dependent on the length of the transition zone and the relative diameters of the balloon and the connected catheter portions, being typically about 10 to 45 degrees. These balloons are prepared by a blow molding operation, wherein the shape of the balloon is governed by the inner shape of the molding chamber of the blow mold. Accordingly, the outer surface of the balloons, at the transition zones, contains an indentation which accounts for the grooves or flutes as defined therein. Finally, it is noted that the central portions of the catheter are directed into a mode of collapse by the flutes which is generally similar to the mode of collapse in the fluted transition zones, wherein the projecting "wings" are then avoided along the entire length of the collapsed balloon catheter.
While the above balloon apparently prevents a flat-collapsed configuration of the balloon, it does not contemplate the advantages of the instant invention, which has found that an extremely small raised ribbed configuration of essentially any geometry on the inner surface of the balloon, wherein the ribs need only maintain some minimal contact angle with the inner balloon wall, can completely prevent a flat-collapsed configuration of the balloon. Furthermore, the ribs as defined run parallel along the entire longitudinal length of the balloon and there is no need to specify a lateral or radial angle of such ribs. Such a design also provides for a much lower profile on any given catheter shaft that the balloon is employed. Moreover, the inner surface configuration described above can be manufactured by extrusion methods.
In accordance with this invention, a balloon configuration for a balloon catheter is provided, which eliminates the undesirable winging phenomena that is encountered when the catheter balloon is in a deflated condition. Also, the catheter balloon is stronger than prior art catheter balloons with improved tensile strength, while exhibiting a reduced wall thickness to improve the flexibility of the balloon. Thus, with the catheter balloon of this invention, balloon catheter procedures can be performed more effectively, with less concern about damage to the patient's veins or arteries by the "winging" phenomena of the deflated catheter balloon, and with ease of catheter advancement through the veins or artery system.
Accordingly, it is the object of this invention to overcome the "wings" using a balloon design that will collapse the balloon evenly around the catheter a full 360 degrees.
It is a further object of this invention to provide a balloon design that is suitable for use with the variety of polymeric materials that are used in dilatation balloon catherization.
Yet a further object of this invention is to provide a balloon design that will collapse the balloon evenly around the catheter a full 360 degrees while at the same time being capable of production via standard plastic melt processing techniques such as extrusion.
Still a further object of this invention is to provide a relatively small, internally ribbed, raised level, triangular, rectangular, square, circular or semi-circular parallel protrusion along the complete longitudinal internal surfaces of the dilatation balloon which can then be employed in a balloon catheter for use in a dilatation procedure such as angioplasty and the like, the internal surface modified balloon catheters being capable of withstanding higher pressures as compared to balloons without internal surface modification, which also serves to provide a lower profile balloon configuration.
These objects, and other objects which will become apparent from the description which follows, are achieved by the balloons and the balloon catheters of the invention and by the methods for their preparation. Thus, in its broadest aspect, the invention comprises balloons and balloon catheters for use in medical dilatation procedures wherein the materials employed for the preparation of the balloons can be altered during their processing and preparation into an elastic balloon configuration that collapses evenly around the surface of a dilatation catheter